feat: add voice status widget showing Claude Code voice input state

[t-benoit]

Summary

• Adds a new voice-status widget that shows whether Claude Code's voice input feature is enabled, read from the user's Claude settings.
• Supports four configurable display formats (icon, icon-text, text, word) plus an optional Nerd Font toggle, modeled on the existing vim-mode widget.
• Reads the effective voice.enabled value from Claude Code's full layered settings stack (project-local → project → user-local → user-global), so the widget reflects the same state Claude Code itself
  uses.

Display

Standard rendering uses a constant 🎤 emoji plus an ASCII state indicator to keep widget width stable:

Format	OFF	ON
icon (default)	🎤 ○	🎤 ◉
icon-text	🎤 off	🎤 on
text	off	on
word	voice off	voice on

With Nerd Font enabled (n in the editor), renders the microphone (U+F130) and microphone-slash (U+F131) glyphs from FontAwesome, providing a natively-differentiated icon for ON vs OFF.

Implementation notes

• New helper getVoiceConfig(cwd) in src/utils/claude-settings.ts reads up to four candidate files in priority order — project-local first, user-global last — and short-circuits on the first one that
  defines voice.enabled. Typical case is a single read; layers without the field don't clobber lower-priority defined values; malformed JSON on a layer is silently skipped (treated as "no override on that
  layer").
• Widget hides itself (render() returns null) when no candidate file exists at all, so users without a Claude installation see nothing rather than a misleading "off".
• The voice.mode field (hold / toggle) is intentionally not exposed — kept available for a possible follow-up widget.

Test plan

• bun test — full suite green (1195 tests; 17 new on getVoiceConfig covering layer precedence, malformed files, missing fields, and CLAUDE_CONFIG_DIR; 31 new on the widget covering all formats ×
  states × Nerd Font modes plus preview / raw value / null-config paths)
• bun run lint — clean
• In the TUI (bun run start): add the Voice Status widget, cycle formats with f, toggle Nerd Font with n, verify preview rendering
• Toggle /voice in Claude Code with the widget visible in the statusline; confirm the rendered state flips between ON/OFF without restart
• Verify graceful behavior when ~/.claude/settings.json is absent or malformed (widget hides, no crash)
• Verify project-local voice.enabled correctly overrides a user-global value (manual: write <cwd>/.claude/settings.local.json with {"voice":{"enabled":false}} while user-global has true,
  confirm widget shows OFF)